Autonomous vehicle steering control relies at least in part on an expected vehicle response based on predetermined inputs to the steering system. It is expected that the vehicle will be able to execute a turn of a particular curvature at a particular vehicle velocity. A problem arises, however, when an expected turning radius cannot be achieved. Such diminished steering system performance may cause an autonomous vehicle to perform in a manner inconsistent with control system commands that presume a fully functional steering system. Diminished steering performance may reduce a curvature, the curvature being an inverse of a turning radius, which a vehicle can accommodate at a particular vehicle velocity.